refactor: Projektstruktur in app/ und backend/ aufgeteilt

app/lib/models/acknowledgment_message.dart

@@ -0,0 +1,85 @@
+/// Acknowledgment message sent by client to confirm message receipt
+class AcknowledgmentMessage {
+  /// ID of the message being acknowledged
+  final String messageId;
+
+  /// Status of the acknowledgment
+  final AcknowledgmentStatus status;
+
+  /// Timestamp when the acknowledgment was created
+  final DateTime timestamp;
+
+  /// Optional error message if status is FAILED
+  final String? errorMessage;
+
+  AcknowledgmentMessage({
+    required this.messageId,
+    required this.status,
+    required this.timestamp,
+    this.errorMessage,
+  });
+
+  /// Create AcknowledgmentMessage from JSON
+  factory AcknowledgmentMessage.fromJson(Map<String, dynamic> json) {
+    return AcknowledgmentMessage(
+      messageId: json['messageId'] as String,
+      status: AcknowledgmentStatus.fromString(json['status'] as String),
+      timestamp: DateTime.parse(json['timestamp'] as String),
+      errorMessage: json['errorMessage'] as String?,
+    );
+  }
+
+  /// Convert AcknowledgmentMessage to JSON
+  Map<String, dynamic> toJson() {
+    return {
+      'messageId': messageId,
+      'status': status.toString(),
+      'timestamp': timestamp.toIso8601String(),
+      if (errorMessage != null) 'errorMessage': errorMessage,
+    };
+  }
+
+  @override
+  String toString() {
+    return 'AcknowledgmentMessage(messageId: $messageId, status: $status)';
+  }
+}
+
+/// Status of an acknowledgment
+enum AcknowledgmentStatus {
+  /// Message was received by the client
+  received,
+
+  /// Message was processed successfully
+  processed,
+
+  /// Message processing failed
+  failed;
+
+  /// Convert string to AcknowledgmentStatus
+  static AcknowledgmentStatus fromString(String value) {
+    switch (value.toUpperCase()) {
+      case 'RECEIVED':
+        return AcknowledgmentStatus.received;
+      case 'PROCESSED':
+        return AcknowledgmentStatus.processed;
+      case 'FAILED':
+        return AcknowledgmentStatus.failed;
+      default:
+        return AcknowledgmentStatus.received;
+    }
+  }
+
+  @override
+  String toString() {
+    switch (this) {
+      case AcknowledgmentStatus.received:
+        return 'RECEIVED';
+      case AcknowledgmentStatus.processed:
+        return 'PROCESSED';
+      case AcknowledgmentStatus.failed:
+        return 'FAILED';
+    }
+  }
+}
+